Semiconductor lasers are attractive for a wide variety of applications including telecommunications, computing systems, optical recording systems and optical connection of integrated circuits. Semiconductor lasers provide a compact source of coherent, monochromatic light which can be modulated at high bit rates to transmit large amounts of information.
Vertical cavity surface emitting lasers (VCSELs) are particularly promising for applications requiring two dimensional arrays of lasers. As contrasted with edge emitting lasers which emit light parallel to the growth planes of their substrates, VCSELs emit light perpendicular to their substrates. A typical VCSEL comprises an active region sandwiched between a pair of distributed Bragg reflector stacks. Upon injection of suitable current through the active region, laser light is emitted perpendicular to the planes of growth.
One difficulty with conventional VCSELs is the absence of polarization control and selectivity for transverse optical modes. As contrasted with edge emitting lasers which have long cavity lengths (100-500.mu.m) and narrow stripe widths (1-10 .mu.m), VCSELs typically have short cavity lengths (200-500 .mu.m) and relatively large transverse circular areas (10-20 .mu.m diameters). The polarization of emitted light is typically defined by accidental fabrication anisotropy and can vary from device to device, even in arrays. Moreover the lasers produce higher order transverse optical output at modest output power and multimode output at high power. The presence of higher modes, however, introduces mode competition noise into the optical output and complicates coupling to optical fiber. Accordingly, there is a need for a vertical cavity laser having enhanced polarization control and transverse mode selectivity.